1. Field of the Invention
This invention relates, in general, to light detectors which detect ambient light and inform a user that the level of a detected ambient light is below a prescribed value. The user may carry out a suitable operation in response to the information from the light detector.
2. Description of Related Art
A light detector may be applied to an automobile. An automobile accident, such as, e.g., collision between automobiles, may occur in the dusk of the evening. This is because it is rather difficult to realize the location of an automobile in such twilight when lamps of the automobile, e.g., headlamp, sidemarker lamp, tail lamp, etc., are not operated. The timing at which the driver turns on the lamp depends on the experimental perception of each driver. Therefore, the timing at which the lamps of an automobile are turned on is different from one to another.
Accordingly, compact and efficient light detectors are needed to inform the driver of the time at which the lamps should be turned on. A conventional light detector includes a light sensor for detecting ambient light, and a light indicator for indicating when a lamp should be turned on. The light sensor and the light indicator are separately arranged with respect to each other to prevent the light sensor from detecting the light from the light indicator when the light indicator is operated. In the above-described conventional light detector, it is difficult to integrally arrange the light indicator and the light sensor on a common base.
The inventors of the present invention attempted to assemble a light indicator and a light sensor on a common base. Firstly, the inventors tried to arrange the light indicator and the light sensor on the same surface of the common base. In this arrangement, light from the light indicator interfered with the operation of the light sensor. The light indicator operates when ambient light detected by the light sensor is below a prescribed level. However, at this moment, the light sensor detects light from the light indicator rather than ambient light, and the light indicator stops its operation immediately after the light sensor detects light from the light indicator. Therefore, the inventors could not visibly observe the operation of the light indicator, because the indicator was on for such a short period. The effect of the light from the light indicator can be avoided if a relatively large isolation wall is arranged between the light indicator and the light sensor. However, the external shape of the light detector becomes relatively large. The inventors also tried to arrange the light indicator and the light sensor on opposite surfaces of the common base. This arrangement could isolate the light sensor from light radiated from the light indicator. However, the external shape of the light detector could not be minimized to a desirable shape.